| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 20°F | 36°F | 27°F | 1.1" |
| February | 26°F | 47°F | 36°F | 0.7" |
| March | 33°F | 58°F | 44°F | 1.2" |
| April | 37°F | 66°F | 51°F | 0.7" |
| May | 45°F | 76°F | 60°F | 1.2" |
| June | 53°F | 86°F | 69°F | 0.7" |
| July | 61°F | 97°F | 79°F | 0.1" |
| August | 57°F | 93°F | 75°F | 0.2" |
| September | 48°F | 83°F | 64°F | 0.4" |
| October | 38°F | 67°F | 51°F | 0.8" |
| November | 29°F | 50°F | 38°F | 1.1" |
| December | 20°F | 37°F | 28°F | 1.8" |
| Index | Harper | Oregon | National |
| Air quality index | 36 | 32 | 42 |
| Pollution index | 1,647,310 | 7,156,356 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 293 |
| Days with moderate air quality | 60 |
| Days w/ poor A.Q. for sensitive groups | 9 |
| Days with unhealthy air quality | 3 |
| Pollutant | Total |
| Arsenic | 0.001% |
| Benzene | 0.010% |
| Carbon Tetrachloride | 0.002% |
| Lead | 0.001% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Harper, OR | 104 | 36 | 28.0% |
| City | Population | Air Quality Index | National Avg. |
| Nolic, AZ | 104 | 47 | 6.0% |
| Moffat, CO | 104 | 16 | 68.0% |
| Garber, IA | 104 | 29 | 42.0% |
| Houghton, IA | 104 | 29 | 42.0% |
| St. Donatus, IA | 104 | 29 | 42.0% |
| Harper, OR | 104 | 36 | 28.0% |
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